Electrical cartridge fuses



0 19.70 J. CINQUIN 3,535,668

' ELECTRICAL CARTRIDGE FUSES Filed July 26. 1968 "Arrows!- I United States Patent 3,535,668 ELECTRICAL CARTRIDGE FUSES Jean Pierre Cinquin, Lyon, France, assignor to Socit Lucien Ferraz & Cie, Lyon, France Filed July 26, 1968, Ser. No. 748,081 Int. Cl. Htllh 85/30 US. Cl. 337-244 3 Claims ABSTRACT OF THE DISCLGSURE In a cartridge fuse having a spring-loaded indicator button retained by an auxiliary wire electrically connected across the terminal caps of the cartridge fuse, so as to The present invention relates to cartridge fuses used for opening an electric circuit in the case of an overload or of a short-circuit.

Conventional cartridge fuses comprise a tubular body of insulating material within which are disposed fusible elements in the form of Wires or strips having their ends soldered to a pair of metallic terminal caps which close the ends of the tubular body. The fusible elements are embedded in a mass of pulverulent arc-extinguishing material. Since it is quite difiicult, if not impossible, to determine visually on an electrical-panel which of the cartridge fuses has blown, it is customary to provide such cartridge fuses with signalling elements. The most commonly used is formed of a spring-loaded indicator button which is retained at a retracted position in a recess of the insulating body by an auxiliary wire the ends of which are electrically connected with the cartridge terminal caps. When the fusible elements have blown, the full voltage is applied to the auxiliary wire which melts or volatilizes, whereby the indicator button is liberated and protrudes from the cartridge body.

The indicator button is generally disposed radially on the periphery of the body of the cartridge fuse, but it may be mounted longitudinally on one of the end caps thereof. It may be used for actuating a microswitch in order to control an alarm circuit or the like.

It has however been observed that under certain conditions the indicator button of a fuse cartridge may fail to operate as expected. This may occur in the case of circuits of quite low voltage in which the current which flows through the auxiliary Wire after the fusible elements have blown may be insufficient to heat this wire up to its melting point. Such is the case for instance with cartridge fuses associated with current rectifying diodes mounted in parallel. When one of these cartridge fuses has blown the voltage across its auxiliary wire may be as low as one volt or less. The wire is not destroyed and the indicator button remains at its normal retracted position although one of the diodes is inoperative. It may also occur that the auxiliary wire only melts locally in a zone far from the button and that the undestroyed portions are retained by friction against the action of the loading spring of the indicator button, as for instance when the auxiliary wire is disposed within the main bore of the cartridge body where it is pressed against the inner side of the latter by the pulverulent arc-extinguishing material.

It is an object of the present invention to provide a cartridge fuse with spring-loaded indicator button wherein the auxiliary wire which retains the button will melt even when the voltage across the cartridge is quite small.

Another object of this invention is to provide a car- 'ice tridge fuse of the kind above referred to, wherein the auxiliary wire will melt in such a zone thereof that the indicator button of the cartridge fuse will be liberated whatever may be the frictional forces applied to the un destroyed portions of the said wire.

According to the present invention, in a cartridge fuse of the kind comprising a spring-loaded indicator button retained at a retracted position by an auxiliary wire electrically connected across the terminal caps of the cartridge fuse, the auxiliary wire is of higher linear ohmic resistance in its zone attached to the indicator button in such manner as to melt in the said zone, even under quite low voltages, when the cartridge fuse has blown.

In the accompanying drawings:

FIG. 1 is a diagram'matical longitudinal section illustrating the general arrangement of a cartridge fuse provided with an indicator button.

FIG. 2 illustrates the auxiliary Wire used in a cartridge fuse according to the invention for retaining the spring loaded indicator button at the retracted position.

FIG. 3 is an enlarged section of the indicator button and of the adjacent portion of a cartridge fuse comprising the auxiliary wire of FIG. 2.

FIG. 4 is a plan view of the indicator button of FIG. 3, its upper cover being supposedly removed.

The cartridge fuse generally illustrated in FIG. 1 comprises a tubular body 1, as for instance of circular cross section, made of an appropriate insulating material, preferably of the ceramic type. The ends of this body are closed by a pair of metallic caps 2 secured in position by screws 3. Each cap is in one with an outer contact member 4, for instance in the form of a blade, and it has an inner boss 2a, these bosses being electrically connected with each other by fusible elements 5, such as silver strips. Elements 5 are embedded in a pulverulent insulating mass 6 which fills the tubular body 1, this mass being made of sand or of any other material having arc-extinguishing properties.

The periphery of body '1 has an outwardly opening recess 1a of substantially cylindrical shape, in which is slidably disposed an indicator button 7 urged outwardly by a spring 8. This button is retained at a retracted position within recess 1a against the action of spring 8 by the central portion of an auxiliary wire 9 which passes through an aperture provided in the bottom of recess 1a, each one of its ends :beng clamped between one end of the tubular body 1 and the corresponding terminal cap 2.

The total ohmic resistance of the auxiliary wire 9 is .rnuch greater than that of the fusible elements 5 and therefore in normal operation the current which flows through the wire is extremely small. But when the fusible elements have blown owing to an overload or shortcircuit, the full voltage of the line is then applied across the said wire which is volatilized. The indicator button 7 is thus liberated and protrudes outwardly under the action of spring 8.

In known cartridge fuses the auxiliary wire '9 is an ordinary wire, made for instance of an alloy of nickel and chromium, having a uniform linear ohmic resistance (or ohrnic resistance per unit of length, as for instance per centimetre). As above explained this known construction has two disadvantages. First, if the voltage which appears across the cartridge fuse when the fusible elements thereof have blown is small, as for instance of the order of 1 volt, wire 9 does not melt and the indicator button fails to operate. The second drawback is that it may occur that the auxiliary Wire is only destroyed locally in a zone far from the indicator button, as for instance in the vicinity of a terminal cap 2 in FIG. 1, in which case its ruptured portion may be retained by friction within the cartridge fuse body, which also results in the indicator button remaining at its retracted position.

In accordanceiwith the present invention the auxiliary wire 9 is s o arranged that its linear ohmic resistance is higher in the zone thereof which is attached to the inclicator button 7, than in the other portions of this wire. -In the preferred embodiment illustrated in FIG. 2, the auxiliary wire is realized under composite form by means of two elementary wires twisted with each other, namely a first elementary wire 10 of relatively high linear ohmic resistance, made for instance of an alloy of nickel and chromium, extending along the full length of the composite wire, and a second elementary wire 11 of relatively low linear ohmic resistance, made for instance of copper or silver, this second elementary wire being interrupted in the central zone A of the composite auxiliary wire 9, which is to be attached to, the indicator button 7. The ends of the two portions of the second elementary wire 11 are soldered to the first elementary wire 10 as indicated at B and C.

It will be understood that with such arrangement the which appears across the cartridge in normal operation,

but it should fully melt as soon as this voltage difference is substantially exceeded.

As illustrated in FIGS. 3 and 4, the indicator button 7 is preferably-in the form of an inverted cup having in its bottom two perforations -7a for passage of the branches of the auxiliary wire 9, the zone A thereof extending between these perforations. The upper side of button 7 is formed witha depression 7b located between perforations 7a in order to avoid that the central portion of zone A 2 may be cooled by contact with-the-button. .The length of zone A is such that the soldered ends C are located in perforations 7a, as shown. The upper end of these perforations 7a are rounded, as indicated at 7c, in order to facilitate sliding of the auxiliary wire 9 (i.e. of the elementary wire 10), when the latter has melted at a point situated substantially above depression 7b, where it is quite free in the air.

.As shown in FIG.,3. there is preferably disposed in a depression of the bottom of the recess 1a of the tubular body 1 a washer 12 made of rubber or similar resilient material and retained in position by the lower end of spring 8. This washer isperforated for passage of the two branches of the auxiliary wire 9 and it forms a seal preventing access of the pulverulent arc-extinguishing material into recess 1a.

A cover 13 is secured onto the indicator button 7 (as for instance by means of an adhesive) in order to prevent projection of molten metallic particles or of flames when the auxiliary wire is volatilized under'the action of a relatively high voltage. Cover 13 and indicator button 7 are preferably made of a refractory material, asfor instance of the ceramic type. a

The invention may of course be applied to cartridge fuses wherein the indicator button is mounted longitudinally in one of the terminal caps. Although the auxiliary wire has been illustrated as disposed in the main bore of the tubular body of the cartridge fuse, it could also be disposed in a separate passage or conduit of small section extending longitudinally through the tubular body.

I claim:

1. A cartridge fuse comprising: I

a tubular insulating body havingtwo open ends;

a pair of metallic end caps each closing one of the ends 4 of said body to form therewith a hollow unit, said unit being formed with an outwardly opening recess; fusible elements within said hollow unit to electrically connect said metallic end caps with each other;

an indicator button movable in said recess of said hollow unit;

spring means to urge said indicator button outwardly of said recess; and

a composite retaining Wire unit under tension along its 7 full length to retain said indicator button in said recess against said spring means, said composite retaining wire unit having two ends, each clamped between one of said metallic end caps and the adjacent end of said insulating body, and an intermediate zone attached to said indicator button, and said composite retaining wire unit including a first elementary wire made of-a material of high specific resistivity, said first elementary wire extending continuously along the full length of said composite retaining wire unit, and a second elementary wire made of a material of low specific resistivity, said second elementary wire being interrupted in said intermediate zone of said composite retaining wire unit, so as to be divided into two portions, each having two ends, with the ends of each of said portions of said second elementary wire being soldered to said first elementary wire.

2. In a fuse cartridge as claimed in claim 1, said first elementary wire being made of an alloy of nickel and chromium and said second elementary wire being made of a metal of the class comprising copper and silver.

3. In a cartridge fuse as claimed in claim 1:

said tubular body having a lateral wall;

said recess being provided in said lateral wall, substantially midway of said ends of said insulating body, said recess having a bottom and said lateral wall having: a perforation opening substantially centrally of said bottom;

said indicator button including an annular portion having a first end and a second end, with said first end of said indicator button facing said bottom of said recess, and a partition to close said second end of said annular portion of said indicator button, said partition having an outer side and an inner side with said outer side being formed with a central depression, and said partition further having two openended holes substantially opposed to each other with respect to said central depression; said composite retaining wire unit being passed through said hole of said bottom, through one of said holes of said partition, across said central depression on the outer side of said partition; through the other one of said holes of said partition, and again through said hole of said bottom; and I said intermediate zone of 'said composite retaining wire unit in which said second elementary wire is interrupted extending substantially on said outer side of said partition between said holes of same.

References Cited UNITED STATESVPATENTS 6/1957 t Brandt et al. 337-244 8/1953 Lebens 337-244 '7/1968 Kozocka 337-244 XR FQREIGN PATENTS 3/1967 Switzerland.

' I 420,350' BERNARD AVGILHEANY, Primary Examiner DEWITT M. MORGAN, Assistant Examiner 

